Electric furnace



Dec; 31, 1968 A. WALZ ELECTRIC FURNACE Sheet 2 of3 Filed March 22, 1967INVENTOR.

A L FRED WA L Z FIG. 2

ATTORNEYS Dec. 31, 1968 A. WALZ ELECTRIC FURNACE Sheet Filed Ilarch 22,1967 FIG. 3

FIG. 4

INVENTOR. ALF/?FD WA L'Z ATTORNEYS United States Patent O 15 Claims. (c.3 23 ABSTRACT OF THE DISCLOSURE An electric furnace for meltingmaterials includes a pair of coaxially arranged symmetrcal electrodesdefining an annular space between them through which the materials to bemelted are passed. To prevent sticking of the material in the sinteringarea the electrodes are maintained at a temperature above the sinteringtemperature of the material throughout their length of contact with thematerial. Where it is desired to form fibers and the like, the moltenmaterial may pass through difuser nozzles supplied with heated air. Ifit is desired to form a com-mon, flowing :melt of material, theindividual strings of molten material may be combined in a funnel-likestructure.

The present invention relates to electric furnaces in general, and moreparticularly to an electric furnace which is especially suited formelting of glass, minerals and other materials by direct resistanceheating. The present invention is an improvement over the electricfurnace disclosed in =my prior United States Patent No. 3,230,29l,granted Jan. 18, 1966.

The electric furnace disclosed in the above mentioned patent consistsessentially of coaxially arranged symmetrical tubes or electrodes, whichtubes at their upper ends are connected to the terminals of an electriccurrent source and which tubes at their lower ends make conductingcontact. An annular space is defined between the tubes through which thematerials to be melted are passed. These materials are supplied to theupper end of the annular space and are steadily heated as they movedownwardly between the tubes until they reach their melting temperature.Outlet openings are provided at the junction of the tubes for the moltenmaterial.

One of the problems encountered in electric furnaces of the typedescribed is the sticking of the material in the region where it hasjust reached the sintering temperature, where it may bake together toform larger particles. consequently the homogeneous supplying ofmaterial in this area is impaired and the risk of obstruction is high.

It is'already known in the prior art to provide shielding cylinders inthis area of sintering temperature. However this not only requiresadditional space in an area where one must employ 'more of the expensiveprecious metals, but the shielded region presents difficulties with thetransfer of heat.

Moreover such electric furnaces may be used for the manufacture offibers and threads by providing discharge nozzles for the moltenmaterial which operate according to the difuser principle. Onedifficulty which has been found for such installation is that the blastof air or other dfiusing medium directs cold air in the blowing nozzlesand which hits the molten material, thereby raising its viscosity toohigh. Especially when the temperature of the molten material when itleaves the furnace is not too high, this quenching of the jet of meltprior to the fiber formation leads to an undesirable action upon theprocess of fi-ber formation.

It may sometimes be desirable to use a furnace of this type for theformation of materials other than fibers or threads. Since a meltingfurnace generally has outlet nozzles in the annular space which arelocated certain distances from each other, generally with compressed airditfusers connected to them, diificulty is experienced in the productionof small amounts of molten glass such as 'would be used for specialpurposes as photographic lens and the like.

Accordingly it is an object of the present invention to provide a newand improved electric furnace which overcomes the above difliculties.

Yet another object of the present inventon is to provide a new andimproved electric furnace which minimizes diificulties created bysticking of the material in the sintering zone.

Yet a further object of the present invention resides in the provisionof an improved electric furnace of the type provided with ditfusernozzles wherein diiculties arising from the increase in viscosity of themolten metal when mixed with cold air of the blowing nozzles isminimized.

Yet a further object of the present invention is the provision of animproved electric furnace of the typedescribed wherein small amounts ofmolten material may be produced which are not fibrous in form.

In accordance with these and other objects there is provided an improvedelectric furnace of the type having a direct, electrical resistanceheating for materials which can be molten and which preferably have ahigh melting point. Such a furnace consists of vertically arranged tubesdefining elect-rodes which preferably are concentric and symmetrical.The upper ends of the tubes are connected to a source of current, andthe lower ends of the tubes make conducting contact. The annular spacebetween the tubes accom modates the material to be molten.

In accordance with one feature of the present invention, the inner tubeis generally cylindrical, and the outer tube is defined by generallycylindrical portions at its upper and lower ends interconnected by anintermediate funnel-shaped portion so that the temperature of the innertube along the region at which it makes contact with the material to bemolten is equal to or higher than the melting temperature of thematerial and that the temperature of the external tube in all of theregion where it makes contact with the material to be molten is higherthan the sintering temperature of the material, and in the regions ofthe outlet nozzles defined at the juncture of the tubes the moltenmaterial will reach at least the melting temperature. Additionally ithas been found that the provision of ar annular hopper concentric withthe tubes and having an annular conical discharge intermediate the tubesnarrower than the space between the tubes will produce a void beneaththe hopper discharge. The temperature gradient along this void will besuch that the tubes where they are engaged at the lower end of the coneof material are above the sintering temperature of the material and thehopper is below the sintering temperature of the material to be molten.

In accordance with another feature of the present invention, the air orfluid supplied to the diifuser nozzles first passes through one of thetubes for cooling the upper portion of the furnace, and thereafter theheated air is supplied to the ditfuser nozzles. Thus the heated air doesnot adversely aifect the viscosity of the molten material passingtherethrough.

In accordance with yet another feature of the present invention, thenozzles formed at the juncture of the inner and outer tubes are of arelatively large diameter and run out into a collecting funnel which islocated underneath the furnace, the streams of molten material being combined in the collecting funnel so as to form one common,

flowing melt which then may be processed further in any known manner.

For a better Understanding of the present invention reference may be hadto the accompanying drawings wherein:

FIG. 1 is `a central vertical section through an electric furnace whichembodies one form of the invention;

FIG. 2 is a central vertical section through an electric furnace whichembodies another form of the invention;

FIG. 3 is a central vertical section through the lower part of amodified furnace; and

FIG. 4 is a central vertical section through the lower part of yetanother modified form of furnace.

Referring now to the drawings, and particularly to FIG. 1 thereof, thereis provided an electric melting furnace formed essentially of twoconcentrical, vertical tubes from a noble metal of a high melting point,.such as platinum or a platinum alloy. More specifically there isprovided an essentially cylindrical internal tube 11 defining an innerelectrode and an external tube 12 defining an outer elec trode, which atits upper and lower end is formed of cylindrical sections of differentdiameters, and which external tube 12 has a funnel-shaped portion in itsintermediate region tapering off from top to bottom. The upper edge ofthe external tube 12. is formed by an outwardly extending flange 13. Attheir lower edges the two tubes 11, 12 are conductingly connected toeach other and are equipped with a crown of outlet nozzles 14 for thedischarge of molten material. The internal tube 11 and the external tube12 are each attached to respective supporting devices by which they aremaintained coaxially.

The supporting device of the external tube 12 is a ring 15 with aninternal face which tapers off conically inwardly and downwardly andwhich is equipped `at its lower edge with an outwardly extending flange16 with bores at its circumference to receive a plurality of attachmentscrews 17. The screws 17 pass through the corresponding holes in thefiange 13 of the external tube 12 and are screwed into thecorresponding, threaded holes of a thrust collar 18. In this way theexternal tube 12 is rigidly connected with the ring 15 forming a goodelectrical contact. The upper, cylindrical section of the ring 15 issurrounded by a clamp collar 19 to which is connected an electrical lead20. The lower internal diameter of the conical ring 15 is smaller thanthe internal diameter of the external tube 12, so that the lower edge 21of the ring 15 protrudes beyond the annular space defined between thetwo tubes 11, 12.

The supporting device of the internal tube 11 consists of an internallyconical screw collar ring 22, the internal diameter of which tapers offupwardly from the outer diameter of the internal tube 11; it is filledin by the internal tube 11, which in this region is equipped with a slit23. The internal tube itself is filled with a tapered shank 24 which hasthe same slope as the collar ring 22. A threaded end 25 of the shank 24protrudes above and beyond the screw collar ring 22, and by aid of atightening nut 26 is braced against the collar ring 22. This clampingproduces both a thermally and an electrically good transition from theinternal tube 11 to the .supporting device. Cooling tubes 27 passthrough the tapered shank 24 and a cooling medium is directedtherethrough. A clamp collar 28, to which a second electrical lead 29 isconnected, surrounds the uppermost, cylindrical end of the tapered shank24. Here too a lower edge 30 of the screw collar ring 22 protrudesbeyond the annular space between the two melting tubes 11 and 12, and isat the same height with the lower edge 21 of the ring 15.

An annular funnel-shaped hopper 31 is formed between the rings 22 and 15concentric with the tubes 11 and 12 and having an annular discharge 33intermediate the rings 11 and 12 and narrower than the space betweenthem and into which material 32 to be molten is poured.

A heat insulating layer surrounds the outer tube and prevents excessivethermal losses.

From the lower funnel discharge 33 the material to be molten drops inthe shape of a freely standing cone 32a of poured material between thetubes 11 and 12, til the goods at the base of this cone make contactwith the tubes.

The cross section through the material between the tu bes 11, 12,through which a current flows, is dimensioned so that the temperature ofthe internal tube 11, where it makes contact with the material to bemolten, is higher than the melting temperature of such material.Preferably the section close to the uppermost contact point at the baseof the cone 3211 of poured material has the highest temperature. Thissimply means that the material to be molten is present as a melt and inthis way make contact with the total surface of the internal tube 11.The best possible heat transfer to the material is created; thus thebest thermal yield is obtained from 'the energy transformed in theinternal tube 11. Furthermore the temperature regulation is very easy,the nelt from the inlet to the outlet nozzles 14 passes over a longenough path as a melt so that it will become degassed and fined.

At the outer cylinder however, the thermal balance shows differentvalues, so that only the lower section which surrounds closely theoutlet nozzles will reach the melting temperature of the batch to bemolten. The temperature upwardly drops but at the base of the cone 32ait is still above the sintering temperature of the material to bemolten. In this way the losses due to radiation towards the outside andthe material to be employed for heat insulation remain within tolerablelimits, and at the same time one prevents the batch sintering in theannular space between the tubes into the shape of large lumps, whichwould stop the flow of material and cause a ruination of the urnace, orat least a stoppage thereof.

On the other hand it is necessary to maintain the temperature of themelting tubes from noble metals so low at the Spots where they areclamped into the supporting parts from an ignoble metal, like aCrNi-steel, that no alloying will occur between these two classes ofmetals. This temperature, as a rule, will be below the sinteringtemperature of the material to be molten. One can bring this about bydirecting water, steam or other fluid against the tapered shank 24.

In this way the material to be melted will leave the hopper 31 whenstill granular and the range of temperatures at which these materialscould become sintered is located in the cone 32a of poured materialwhich stands free so that no flow of material will become interrupted.

With a PtRh alloy with about Pt and 20% Rh the temperature at the outletnozzles 14 is in the range of 1400 C. to 1500 C. The hottest spot of theinternal cylinder lies close to the base of the cone of poured materialand is about 1600 C. The critical temperature at which the noble metalbecomes alloyed With the ignoble metal of the supporting device will beabout 600 C. Therefore one must bring about orcefully inside theinternal tube 11 a temperature drop of about 1000 C. in the region ofthe freely standing cone 32a of poured material. The conditions for thehandling of the outer tube are not so complicated. On the other hand theinternal tube must be protected against overheating 'and melting, and ifdesred a thermocouple transmitter (not drawn) may be used at the hottestpoint of the internal tube, which switches off the installation as soonas the maximum permissible temperature is overstepped, i.e.approximately 1700 C.

The heat which flows from the supporting device goes automaticallyupwardly and will then become exploited for the preheating of thematerial in the funnel tube (not shown), and this too is a featurebeneficial for the overall performance of the melting furnace.

As previously described, the melting furnace 38 consists essentially oftwo concentrical, vertical tubes 11, 12 from a noble metal of a highmelting point, preferably Pt or a Pt alloy. The two tubes 11, 12 attheir lower ends are connected with each other in an electricallyconducting manner, and are equipped with a crown of outlet nozzles 14for the molten goods. The internal tube 11 and the external tube 12 attheir upper ends are each attached to a supporting device in the mannerheretofore described and in this way are kept coaxial. The supportingdevice of the external tube includes the ring 15 around which a thrustcollar 19 is placed. An electric lead 20 is Secured to the thrust collar19. The supporting device of the internal tube 11 includes a conicalbolt or tapered shank 39 which functions in the same manner as thetapered shank 24 described in the embodiment of FIG. 1. At the upper endof the conical bolt 39 is the clamping ring 28 which provides theconnection for the second electric lead 29. The conical bolt 24 alongits jacket surface is equipped with an helical cooling channel 42, whichat its upper end is connected with the supply tube 27 for the coolant,and at its lower end is connected with a discharge tube 43 for thecoolant. The external tube 12 from a no ble metal along its full lengthis equipped with the insulation jacket 3-1.

The removal tube 43 for the coolant is guided concentrically inside theinternal tube to the lower end thereof and protrudes below beyond theopening of the internal tube 11, so that it may support an annularditfuser discharge nozzle 44. This discharge nozzle 44 consists of theinternal body 45 with rotation symmetry, -which is attached at the lowerend of the discharge tube 43, and which has the shape of an urn, with arounded-off, upper edge covered by a lid or plate 46. Between the edgeof the urn structure and the lid 46 is defined an annular slot 47 forthe removal of the heated cooling gas. The inside of the internal body45 of the discharge nozzle is connected to the inside of the removaltube 43 by a plurality of holes 48 in the tube wall.

The external 'body of the discharge nozzle 44 is made up of acylindrical annular sheath 49 which surrounds the internal body 45 inspaced relation. A jacketing 50` is located beyond and above the upperedge of the sheath 49 to define an annular slot 51. If the externalsupporting ring 15 is equipped With cooling Channels, then this air too,which became preheated in this external supporting device, may bedrected to the ditfuser discharge nozzle 44.

By means of the airfiow through the ring-shaped (annular) slots 47 and51 into the annular jet slot, the molten material is first suoked in inthe form of filaments and then, by means of turbulence, is separatedinto many individual filaments of very small diameter. By means of theunique enlargement of the difi'usor, and after the specificdisintegration into filaments, the flow velocity is considerablydiminished thereby improving the eficiency of the areodynamic effect.

In the embodiment of FIG. 3, the discharge (removal) tube 43 for thecoolant, which runs concentrcally inside the internal tube 11 of amelting furnace, is closed by a plate 61 at its lower end whichprotrudes beyond the lower opening of the internal tube. Bores 62 arelocated in the cylinder wall of the discharge tube 43 at approximatelythe height of the outlet openings 14. The heated cooling gas is blownfrom the bores 62 against the streaming threads of melt, so that theyare propelled outwardly in t-he shape of beads or little spheres.

In the embodiment of FIG. 4, there is provided a modified form ofelectric melting furnace adapted to provide a continuous flow of moltenmaterial. As therein illustrated, an improved melting furnace consistsessentially of the two concentric, vertical tubes 11', 12' which aresimilar to the tubes 11, 12 heretofore described except as t-o themanner of jointer at their lower ends. At their lower edges the twotubes 11', 12' are connected to each other in an electrically conductingmanner, as by a ring or rim 65 provided with a plurality of outletopenings 14' for the molten goods.

The supporting of the internal tube 11' 'and of the external tube 12'and the manner of heating of the furnace 6 occurs as previouslydescribed for the embodiments of FIGS. 1, 2 and 3.

According to the present invention, a collecting funnel 66 is placed atthe lower edge of the outer tube 12. This funnel 66 catches the meltedstreams which leave the outlet openings 14', combines them anddischarges them at its outlet 67 as a common flow of melt. The diametersof the outlet openings 14' thereby are dimensioned so that the melt runsout of the furnace solely under the action of gravity; there is nonozzle effect. For melts of ordinary glass a diameter of about 2 mm. andmore was found suitable for the discharge openings 14'. In order tobring about a good heat retention inside the funnel 66, it may besurrounded by a thermal insulation.

The flow of melt which leaves the outlet 67 of the funnel 66 may bepassed into a processing machine, as this is commonly done.

Although the present invention has been described in conjunction withpreferred embodiments thereof, it is obvious that numerous otherembodiments may be devised by those skilled in the art. It is thereforeintended in the appended claims to cover all such modifications as fallwithin the true spirit and scope of this invention.

What is claimed as new and desired to be Secured by Letters Patent ofthe United States is:

1. In a melting furnace of the type having direct electrical resistanceheating for melting material and formed by vertically arrangedconcentric tubes defining electrodes, the tubes making conductingcontact at their lower ends and provided with discharge nozzles at theirjunction, an annular space being defined between the tubes toaccommodate the material to be melted; the improvement wherein the innertube is generally cylindrical, and the outer tube is defined bygenerally cylndrical portions at its upper and lower ends interconnectedby an intermediate funnelshaped portion so that the temperature of theinternal tube along the full region at which it makes contact with thematerial to be melted is equal to or higher than the melting temperatureof the material, and the temperature of the external tube in all of theregion where it makes contact with the material to be melted is higherthan the sintering temperature of the material, and in the region of thedischarge nozzles the material will reach at least the meltingtemperature.

2. The improvement in a melting furnace as set forth in claim 1 whereinthe temperature at the uppenmost point of contact between the materialto be melted and said tubes is higher than the temperature close to thedischarge nozzles.

3. The improvement in a melting furnace as set forth in claim 1 whereinsaid tubes are formed of platinum or of a platinum alloy.

4. The improvement in a melting furnace as set forth in claim 3including support means supporting each of said tubes near their upperend and formed of ignoble metal the temperature of said tubes at saidsupport means being less than the temperature at which said ignoblemetal would become alloyed with the metal of said tubes.

5. The improvement in a melting furnace as set forth in claim 4 abovewherein the support means for at least one of said tubes is providedwith forced cooling means.

6. In a melting furnace of the type having direct electrical resistanceheating for melting materials and fonmed by vertically arrangedconcentric tubes defining electrodes, the tubes making conductingcontact at their lower ends and provided with discharge nozzles at theirjunction, an annular space being defined between the tubes toaccommodate the material to be melted;

the improvement including an annular hopper concentrically positionedvertically above said tubes and havin-g an annular dischargeintermediate said tubes and narrower than the space between said tubesso that a void is created between said hopper discharge and the upperside walls of said tubes.

7. The improvement in a melting furnace as set forth in claim 6 whereinthere is formed 'an annular cone of poured material to be meltedextending from said hopper discharge, said void providing an area in theside walls of said tubes having a temperature gradient such that thetemperature of the tubes where they are engaged by the lower end of saidcone is above the sintering temperature of said material and thetemperature of said hopper is maintained below the sintering temperatureof said material.

8. In a melting furnace of the type having direct electrical resistanceheating for melting material and formed by vertically arrangedconcentric tubes defining electrodes, the tubes making conductingcontact at their lower ends and provided with discharge nozzles at theirjunction, an annular space being defined between the tubes toaccommodate material to be melted; the improvement comprising blastnozzles for directing a flow of fluid into the flow of molten materialfrom said discharge nozzles, cooling means for the upper end of at leastone of said tubes where it is supported, and a removal line from saidcooling means extending through the inner one of said tubes and throughthe lower end thereof connected to said blast nozzles to serve as asupply line for the blast air to said blast nozzles.

9. The improvement in a melting furnace as set forth in claim 8 whereinsaid removal eonduit protrudes below the discharge nozzles for themolten material in said furnace and carries at its protruding end ahollow symmetrical hub provided with an annular slot, and an annularsheath around said hub defining a diffuser nozzle common to all thedischarge nozzles.

10. In a melting furnace of the type having direct electrical resistanceheating for melting materials and formed by vertically arrangedconcentric tubes defining electrodes, the tubes making conductingcontact at their lower ends and provided -with discharge nozzles attheir junction, an annular space being defined between the tubes toaccommodate the material to be melted; the improvement defining a blastnozzle below said discharge nozzles for directing a flow of fluid intothe outflow of molten material from said outflow nozzles, means forproviding blast fluid to said blast nozzle, a hollow symmetrical hubbeing provided with an annular slot, and an annular sheath encirclin-gsaid hub' to form a diffuser nozzle which is common to all the furancedischarge nozzles.

11. In a melting furnace as set forth in claim 10 including means fordirecting preheated air into said blast nozzle.

12. In a mixing furnace of the type having direct, electrical resistanceheating for melting materials and formed by vertically arrangedconcentric tubes defining electrodes, the tubes making conductingcontact at the lower ends and provided with discharge nozzles at theirjunction, an annular space being defined between the tubes toaccommodate the material to be melted; the improvement including a blastnozxzle for directing a flow of fluid into the outflow of moltenmaterial from said discharge nozzles, said blast nozzles including aremoval line extending through the inner one of said tubes andprotruding below the outflow nozzles of the melting furnace, saidremoval line being closed at its bottom end and provided with aplurality of bores spaced across the periphery of its cylindrical walland located at approximately the height of said discharge nozzles.

13. In a melting furnace of the type having direct electrical resistanceheating for melting material and forrned by Vertically arrangedconcentric tubes defining electrodes, the tubes making conductingcontact at their lower ends and provided with discharge nozzles at theirjunction, an annular space being defined between the tubes toaccommodate the material to be melted; the improvement comprisng acollecting funnel placed underneath the furnace in the path of the flowfrom said discharge nozzles, said discharge nozzles having a crosssectional area sufficent to permit gravity flow of molten materialtherethrough.

14. The improvement in a melting furnace as claimed in claim 13 whereinthe upper edge of said collecting funnel is connected to the lower edgeof the outermost one of said tubes.

15. The improvement in a meltin-g furnace as claimed in claim 13 whereineach of said disc'harge nozzles have a diameter of at least 2 mm.

References Cited UNITED STATES PATENTS 2,233,435 3/1941 Snow 13-62,350,829 6/1944 Scharfnagel 13--6 X 2,600,490 6/1952 De Voe 13--342,680,772 6/ 1954 Skinner et al 13-34 3,109,045 10/1963 Silverman 13--63,230,29l 1/1966 Walz 13-6 3,212,871 10/1968 Vattrodt 13-6 X BERNARD A.GILI-IEANY, Primary Examiner.

H. B. GILSON, Assistant Exam'ner.

U.S. Cl. X.R.

